1. Field of the Invention
The present invention relates to a semiconductor device manufacturing substrate which has an SOI (silicon on insulator) structure, and a method for manufacturing the semiconductor device manufacturing substrate.
Note that a semiconductor device in this specification refers to all types of devices which can function by utilizing semiconductor characteristics, and electro-optic devices, semiconductor circuits, and electronic devices are all included in the category of the semiconductor device.
2. Description of the Related Art
With development of VLSI technology, lower power consumption and higher speed over the scaling law which can be realized by bulk single-crystal silicon have been demanded. In order to meet these demands, an SOI structure has been attracting attention. This technology allows an active region (channel formation region) of a field effect transistor (FET), which has been formed of bulk single-crystal silicon, to be formed of a single-crystal silicon thin film. It is known that a field effect transistor manufactured using an SOI structure has lower parasitic capacitance than a field effect transistor manufactured using a bulk single-crystal silicon substrate, which is an advantage in increasing speed.
A SIMOX substrate or a bonded substrate is known as an SOI substrate. An SOI structure of a SIMOX substrate is obtained in such a manner that oxygen ions are implanted into a single-crystal silicon substrate and heat treatment is performed at greater than or equal to 1300° C. to form a buried oxide film, and accordingly a single-crystal silicon film is formed on the surface. As for a SIMOX substrate, oxygen ion implantation can be controlled precisely, and thus a single-crystal silicon film with a uniform thickness can be formed; however, there are time and cost problems because a long period of time is needed for oxygen ion implantation. In addition, there is another problem in that a single-crystal silicon substrate is likely to be damaged during oxygen ion implantation, which has an influence on a single-crystal silicon film to be obtained.
An SOI structure of a bonded substrate is obtained in such a manner that two single-crystal silicon substrates are bonded to each other with an insulating film interposed therebetween and one of the two single-crystal silicon substrates is thinned to form a single-crystal silicon film. As a thinning method, a hydrogen ion implantation separation method is known. A hydrogen ion implantation separation method is a method in which hydrogen ions are implanted into one single-crystal silicon substrate to form a microbubble layer at a predetermined depth from the silicon substrate surface, a thin single-crystal silicon film can be bonded to the other single-crystal silicon substrate with use of the microbubble layer as a cleavage layer (see Patent Document 1: Japanese Published Patent Application No. 2000-124092).
In recent years, there has been an attempt to form a single-crystal silicon film over a substrate with an insulating surface, such as a glass substrate. For example, an SOI substrate in which a single-crystal silicon film is formed over a glass substrate disclosed by the present applicant is known as an example (see Patent Document 2: Japanese Published Patent Application No. H11-163363).